The present invention relates to orthodontic brackets and more particularly to brackets adapted for placement on the inner, i.e., lingual or palatal, sides of teeth.
Braces have long been used for straightening teeth. In general, this method of straightening teeth calls for connecting a resilient wire to the teeth by means of brackets individually attached to the teeth. Formerly, such brackets were universally applied to the outer or labial sides of the teeth, as disclosed in U.S. Pat. No. 3,076,265 to Moore and in FIG. 1 of U.S. Pat. No. 4,209,906 to Fujita. Recently, it has become common to apply the brackets to the inner of lingual sides of the teeth, thereby hiding the braces from view. A suitable method for applying braces to either the labial or the lingual sides of the teeth is disclosed in my prior U.S. Pat. No. 3,842,503.
A continuing problem in orthodontia is how best to secure arch wires to the teeth. A variety of brackets have been proposed for this purpose. One conventional form of bracket, disclosed in FIG. 3 of the Fujita patent, is commonly referred to as the "edgewise" bracket. This bracket has a unitary body having a central arch wire slot and a pair of oppositely-directed wings. An arch wire is secured in the slot by means of a wire ligature or an elastomer O-ring. This design is used on the labial side of the teeth and is not designed for use on the lingual side. Securing the arch wire in a slot with a ligature on the labial side is impractical because of the difficulties of twisting the ends of the ligature wire together, particularly inside the mouth, and of injury to soft tissues by the wire ends. Using elastomer O-rings, or elastics, in lieu of ligature wires is also impractical, particularly for securing an arch wire to the lingual sides of the front teeth. Frequently, the straightening force to be applied to the front teeth is such that an O-ring cannot hold the arch wire securely in the slot of a single bracket. This problem is most acute when it is necessary to apply torsion about the axis of a tooth. Two brackets are sometimes mounted side by side on a tooth to apply greater torque. However, the lingual sides of the front teeth are usually too narrow to affix two brackets.
Variations of the edgewise bracket are disclosed in U.S. Pat. Nos. 4,023,274 to Wallsheim and 4,227,876 to Fogel, et al. However, the latter designs are no more practical than the basic edgewise bracket for use on the lingual sides of the teeth.
Another form of bracket, disclosed in FIG. 4 of the aforementioned Fujita patent, employs an arch wire slot positioned so that a wire may be inserted vertically from the opposite side of the occlusal plane, that is, from the root of the tooth toward the biting surface. Variations of this bracket are disclosed in my prior U.S. Pat. Nos. 3,748,740 and 3,854,207. This approach is not conveniently applicable to the lingual sides of the teeth because of the difficulties of inserting an arch wire into the bracket behind the teeth.
The aforementioned Fujita patent attempts to overcome some of the foregoing difficulties by proposing a lingual bracket in which the arch wire is held in a slot by means of a U-shaped spring clip. Referring to FIG. 6 of Fujita, two different kinds of bracket are used. In one kind of bracket, the slots open in a vertical direction toward the occlusal plane for use on the upper teeth. In the other kind of bracket, the slots open rearwardly, parallel to the occlusal plane, particularly for use on the lower teeth. It would be preferable to be able to use the same kind of bracket on both upper and lower teeth. A major drawback of the Fujita design is that the brackets rely primarily on the spring tension of the U-shaped clip to retain the arch wire in place. Difficulties in seating a twisted or bent arch wire squarely in the slot may make it virtually impossible to secure it with such a locking member. A further difficulty arises from the fact that the locking member is separate from the body of the bracket and, being quite small, can easily be lost in the patient's mouth while emplacing or replacing arch wires.
My prior U.S. Pat. No. 3,780,437 discloses a bracket in which the arch wire is held in a slot in the bracket body by a finger of a rigid U-shaped sliding closure member or follower. The finger has a camming portion adapted to push the arch wire downwardly into the slot as the follower is moved normal to the depthwise dimension of the slot. The follower is also connected to the bracket body by means of a snap ring which surrounds the bracket body and engages shoulders of the follower between its ends to hold the follower weakly in an open position and more strongly in a closed position. However, it is not always possible or desirable to fully seat the arch wire in its slot. Under certain circumstances, it is desirable to be able to secure the arch wire to the bracket in a position only partially seated in the slot, for example, at a depthwise angle in the slot. However, like the brackets of Fujita, this bracket does not afford a capability of partially closing the follower.
U.S. Pat. No. 4,248,588 to Hansen discloses a bracket generally similar to that of my aforementioned U.S. Pat. No. 3,780,437, except that the closure member is a resilient rather than a rigid member. Hansen also dispenses with the need for a snap ring by forming the body of the bracket so as to hold the closure member in an open and a closed position without separating it from the body. The resiliency of the member allows somewhat more flexibility in seating a bent arch wire in the slot, but does not enable it to be positioned to partially close the slot. It remains necessary to seat the wire most of the way into the slot so that it can be resiliently clamped between the legs of the follower as shown in FIG. 8 of Hansen. It would be preferable to be able to secure the arch wire to a bracket even if it cannot be seated in the slot. From FIG. 8 of Hansen, it is apparent that this goal can only be accomplished in the bracket of Hansen by using a ligature wire. As previously discussed, using such a wire is undesirable because of the difficulties of working with wire on the lingual side of the teeth, as well as the discomfort of wire ends to the soft tissues of the mouth.
In addition, both the bracket of my prior U.S. Pat. No. 3,780,437 and the bracket of Hansen are designed for use on the labial sides of the teeth. The labial sides of the teeth are essentially parallel to the axes of the teeth and, when the teeth are properly positioned, approximately normal to the occlusal plane. Hence, the arch wire slot opens frontally, normal or, as disclosed in Hansen, at slight angular variations from normal to the labial sides of the teeth, and the follower channel is essentially normal to the slots. This arrangement cannot be conveniently applied to the inner sides of the teeth, particularly to the palatal sides of the upper teeth. The inner sides of the teeth are inclined so as to intersect the occlusal plane at a large acute angle, typically of about 55.degree., but commonly varying over a range of 30.degree. to 80.degree.. This problem is acknowledged in Fujita at FIG. 6, which shows a palatal bracket opening downwardly, perpendicularly to the occlusal plane. However, as noted above, the approach of Fujita is preferably to be avoided because it requires two types of brackets. Fujita also acknowledges, in column 5, that insertion of the arch wire parallel to the occlusal plane presents some difficulties in operation and may cause deformation of the arch wire, which is desirably avoided. Thus, the problem remains of how best to position an arch wire slot and its closure means in a lingual bracket.
Accordingly, a need remains for an orthodontic bracket which overcomes the foregoing problems and limitations.